CVE-2016-0753.yml

---
gem: activemodel
framework: rails
cve: 2016-0753
date: 2016-01-25
url: "https://groups.google.com/forum/#!topic/rubyonrails-security/6jQVC1geukQ"

title: Possible Input Validation Circumvention in Active Model 

description: |
  There is a possible input validation circumvention vulnerability in Active 
  Model. This vulnerability has been assigned the CVE identifier CVE-2016-0753. 

  Versions Affected:  4.1.0 and newer 
  Not affected:       4.0.13 and older 
  Fixed Versions:     5.0.0.beta1.1, 4.2.5.1, 4.1.14.1 

  Impact 
  ------ 
  Code that uses Active Model based models (including Active Record models) and 
  does not validate user input before passing it to the model can be subject to 
  an attack where specially crafted input will cause the model to skip 
  validations. 

  Vulnerable code will look something like this: 

  ```ruby 
  SomeModel.new(unverified_user_input) 
  ``` 

  Rails users using Strong Parameters are generally not impacted by this issue 
  as they are encouraged to whitelist parameters and must specifically opt-out 
  of input verification using the `permit!` method to allow mass assignment. 

  For example, a vulnerable Rails application will have code that looks like 
  this: 

  ```ruby 
  def create 
    params.permit! # allow all parameters 
    @user = User.new params[:users] 
  end 
  ``` 

  Active Model and Active Record objects are not equipped to handle arbitrary 
  user input.  It is up to the application to verify input before passing it to 
  Active Model models.  Rails users already have Strong Parameters in place to 
  handle white listing, but applications using Active Model and Active Record 
  outside of a Rails environment may be impacted. 

  All users running an affected release should either upgrade or use one of the 
  workarounds immediately. 

  Releases 
  -------- 
  The FIXED releases are available at the normal locations. 

  Workarounds 
  ----------- 
  There are several workarounds depending on the application.  Inside a Rails 
  application, stop using `permit!`.  Outside a Rails application, either use 
  Hash#slice to select the parameters you need, or integrate Strong Parameters 
  with your application. 

  Patches 
  ------- 
  To aid users who aren't able to upgrade immediately we have provided patches for 
  the two supported release series. They are in git-am format and consist of a 
  single changeset. 

  * 4-1-validation_skip.patch - Patch for 4.1 series 
  * 4-2-validation_skip.patch - Patch for 4.2 series 
  * 5-0-validation_skip.patch - Patch for 5.0 series 

  Please note that only the 4.1.x and 4.2.x series are supported at present. Users 
  of earlier unsupported releases are advised to upgrade as soon as possible as we 
  cannot guarantee the continued availability of security fixes for unsupported 
  releases. 

  Credits 
  ------- 
  Thanks to: 

  [John Backus](https://github.com/backus) from BlockScore for reporting this! 

unaffected_versions:
  - "<= 4.0.13"

patched_versions:
  - "~> 5.0.0.beta1.1"
  - ">= 4.2.5.1"
  - "~> 4.1.14.1"